Exhaust systems are often used to remove pollutants from a conditioned space. Many of these systems handle aerosols that are imperfectly removed from exhausted air streams permitting the deposit, and accumulation, of materials in exhaust ducting and hoods. For example, kitchen range hoods remove cooking fumes from kitchens. Such fumes often contain grease aerosols that are imperfectly filtered using grease filters. After a long period of operation, some grease inevitably coats the inside of exhaust ductwork. This can pose a fire hazard and have other undesirable consequences.
There are many devices that have been designed and manufactured for removal of fumes from a kitchen. Canopy and backshelf hoods are common types. These are typically situated above a cooking appliance or appliances and connected through an exhaust duct to a roof-mounted fan that draws air through the hood and discharges to the outside ambient air. Removable cartridge grease filters are usually mounted in the hood just preceding the ductwork. These are normally removed periodically from the hood and washed to remove accumulated grease. Such filters are imperfect in that they are effective for removing the largest particulates, but they tend to leave a substantial amount of grease in the exhausted stream. Grease passing the filters accumulates in the ductwork from the hood and can accumulate on the fan and discharge of the exhaust system as well.
Once grease builds up in a duct, it is possible to clean the duct. Various systems for doing this are known. Visual inspection is one means of determining whether a duct is in need of cleaning. Another method of detecting buildup is described in U.S. Pat. No. 3,890,827 for “Method and apparatus for monitoring grease buildup within an exhaust system” which describes removable patches that can be installed in a duct and removed for close inspection to determine how much grease has accumulated on the surface. Multiple patches are mounted as a set and one patch is removed at a time to determine the grease accumulation.
Fire detection and elimination is a well-known solution for exhaust hoods and ducts. Conventional fire detection and suppression systems may be in installed in kitchen exhaust hoods and ductwork. Fire can be suppressed using water or chemical extinguishers. For example, U.S. Pat. No. 4,524,835 for “Fire suppression system” describes a chemical fire suppression system
There is a need in the art for convenient and reliable mechanisms for detecting the buildup of grease and other contaminants in ductwork. The known methods relying on visual inspection are tedious and unreliable and also difficult to enforce.